REJOICE: Scientist Says Dirt Is Good for Kids

Parents sterilize their kids' pacifiers, toys and hands, but all that cleaning could be wreaking havoc on children's immune systems, according to a University of Chicago scientist who specializes in microbial ecosystems.

Modern society's indoor living and sterilized surfaces are nothing like our ancestors' outdoor existence. That difference can cause our immune systems to become hyper-sensitized, Gilbert told NPR in a recent interview.

"You have these little soldier cells in your body called neutrophils, and when they spend too long going around looking for something to do, they become grumpy and proinflammatory," he explained. "When they finally see something that's foreign, like a piece of pollen, they become explosively inflammatory. They go crazy. That's what triggers asthma and eczema and often times, food allergies."

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Gilbert references past research about dropped pacifiers to prove his point. Parents who "cleaned" them by popping them in their own mouths were less likely to have kids with allergies later on compared to other methods, according to a 2013 study published in Pediatrics. The Swedish scientists suspected that the harmless bacteria from moms' saliva stimulated their children's immune systems, building up their defenses.

The "five-second rule" is another chance for a potential boost. While microbes will latch onto fallen food in milliseconds, it's "virtually impossible" any dangerous pathogens will hitch a ride as well, Gilbert says. He even goes as far to say that dirt from the backyard or a lick from the family dog isn't as dangerous as most parents think. The exposure could even help kids' health in the long run.

"Hand washing may be the single most important act you and your child have for disease prevention," the AAP says. "The best solution is to wash your child's hands with warm water and ordinary soap that does not contain antibacterial substances."

That includes after going to the bathroom, playing outside, touching animals or sneezing or coughing. Kids should also wash up before eating, or whenever someone at home is ill. At the end of the day, parents should definitely encourage proper hygiene at home — but maybe worry a little bit less about sterilizing the entire playroom.